4-Appendix A.2 Geotechnical Design Report Hwy462.pdf

GEOTECHNICAL

DESIGN REPORT

Beaufort – Jasper Water and Sewer Authority

Chelsea Canal Critical Crossings Improvement

Crossing at Highway 462

Jasper County, South Carolina

May 3, 2024

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Beaufort – Jasper Water and Sewer Authority

Chelsea Canal Critical Crossings Improvement

Crossing at Highway 462

Geotechnical Design Report

May 3, 2024

Prepared by: Prepared by:

Daniel C. Pitts Thomas E. Evans, P.E.

Geotechnical Engineer Geotechnical Engineer

License No. 33058

Reviewed by:

Danielle Neamtu, P.E., PMP

Geotechnical Engineer

Tommy Evans (Geo)

COA

Tommy Evans (Geo) Stamp i

Table of Contents

Abbreviations ...................................................................................................................... i

Section 1 Introduction ..................................................................................................... 1-1

1.1 Project Description .................................................................................................................................................. 1-1

1.2 Elevation Datum ........................................................................................................................................................ 1-1

1.3 Purpose and Scope ................................................................................................................................................... 1-1

1.4 Report Limitations ................................................................................................................................................... 1-1

Section 2 Site and Subsurface Conditions ......................................................................... 2-1

2.1 Site Conditions ........................................................................................................................................................... 2-1

2.1.1 General ............................................................................................................................................................. 2-1

2.1.2 Regional Geology ......................................................................................................................................... 2-1

2.2 Subsurface Investigation Program .................................................................................................................... 2-1

2.2.1 Field Exploration ......................................................................................................................................... 2-1

2.2.2 Geotechnical Laboratory Test Results ............................................................................................... 2-2

2.3 Subsurface Conditions ............................................................................................................................................ 2-3

2.3.1 General ............................................................................................................................................................. 2-3

2.3.2 Subsurface Conditions .............................................................................................................................. 2-3

2.4 Expected Variations in Subsurface Conditions ............................................................................................ 2-4

Section 3 Geotechnical Engineering Evaluation and Design Recommendations ................. 3-1

3.1 General .......................................................................................................................................................................... 3-1

3.2 Foundation Design Recommendations ........................................................................................................... 3-1

3.2.1 General ............................................................................................................................................................. 3-1

3.2.2 Seismic Hazard Analyses ......................................................................................................................... 3-1

3.2.3 Over-excavation and Replacement ...................................................................................................... 3-1

3.2.4 Excavation Backfill ..................................................................................................................................... 3-2

3.2.5 Corrosion Considerations ........................................................................................................................ 3-2

3.3 Pavement Replacement.......................................................................................................................................... 3-2

3.4 Sheet Pile Wing-Walls ............................................................................................................................................. 3-3

Section 4 Construction Considerations ............................................................................. 4-1

4.1 General .......................................................................................................................................................................... 4-1

4.2 Excavation and Excavation Support ................................................................................................................. 4-1

4.3 Dewatering .................................................................................................................................................................. 4-1

4.4 Protection and Preparation of Subgrade Soils ............................................................................................. 4-2

4.5 Protection of Adjacent Structures ..................................................................................................................... 4-2

4.5.1 General ............................................................................................................................................................. 4-2

4.6 Backfill ........................................................................................................................................................................... 4-3

4.6.1 Structural Fill ................................................................................................................................................ 4-3

4.6.2 Common Fill and Select Common Fill ................................................................................................. 4-3

4.6.3 Crushed Stone ............................................................................................................................................... 4-3

4.7 Geotextile Fabric ....................................................................................................................................................... 4-4

Table of Contents ii

4.8 Construction Monitoring ....................................................................................................................................... 4-4

List of Figures

Figure 1-1 Project Locus ..................................................................................................................................................... 1-3

Figure 1-2 .................................................................................................................................................................................. 1-4

List of Tables

Table 2-1 Geotechnical Laboratory Index and Corrosion Test Results .......................................................... 2-5

Table 2-2 Subsurface Investigation Program ............................................................................................................ 2-7

Table 4-1 Structural Fill Gradation .................................................................................................................................... 4-3

Appendices

Appendix A – Test Boring Logs and Legend

Appendix B – Geotechnical Laboratory Test Results i

Abbreviations

1H:1V 1 horizontal to 1 vertical

ASTM American Society of Testing and Materials bgs below ground surface

Cl chloride content

DIP ductile iron pipe

El. elevation

GDM Geotechnical Design Manual

HWY 462 State Highway 462 kip kilopound lf linear feet

NAVD 88 North American Vertical Datum of 1988

OSHA Occupational Safety and Health Administration

PCBC Precast Concrete Box Culvert pcf pounds per cubic feet pci pounds per cubic inch psf pounds per square foot

ROW Right-of-Way

SCI Soil Consultants, Inc.

SCDOT South Carolina Department of Transportation

SO4 sulfate content

SPT

Standard Penetration Test

Acronyms ii

1-1

Section 1

Introduction

1.1 Project Description

CDM Smith is providing design, permit, and bid phase services to Beaufort-Jasper Water and

Sewer Authority (BJWSA) related to the proposed Chelsea Canal Critical Crossings (C4)

Improvements. The proposed Crossing is in Jasper County 10.5 miles northeast of Hardeeville, South Carolina. The project locus is shown in Figure 1-1.

The project consists of replacing the existing pipe culverts under Highway 462 with 8-ft by 4-ft

Precast Concrete Box Culverts (PCBC) installed at the location and depths shown on the contract drawings.

The proposed structure is shown on Figure 1-2.

1.2 Elevation Datum

All elevations (El.) noted herein are in feet and referenced to the North American Vertical Datum of 1988 (NAVD 88).

1.3 Purpose and Scope

The purpose of this report is to summarize the subsurface conditions encountered during the geotechnical investigation program and provide geotechnical engineering recommendations for design and construction. Specifically, the scope of work included the following:

Drill three (3) test borings (B-4, B-5, and B-6) near the intersection of the BJWSA Canal and

Highway 462 to depths of 20 to 50 feet below ground surface (bgs).

Conduct geotechnical laboratory testing on select soil samples to assist with classification and estimate the engineering properties of the materials.

Review available and relevant information and subsurface conditions encountered during the geotechnical investigation.

Perform geotechnical analyses and develop geotechnical engineering recommendations for design and construction of the canal crossings.

Prepare Geotechnical Engineering Report presenting CDM Smith’s recommendations and construction considerations for the C4 Improvements project.

1.4 Report Limitations

This Geotechnical Report has been prepared for the C4 Improvements project at the Highway 462 crossing in Jasper County, South Carolina, as understood at this time and described in this report.

The report has been prepared in accordance with generally accepted engineering practices.

Section 1 • Introduction

1-2

Additionally, many requirements of the SCDOT 2022 GDM were observed, due to sampling taking place within the ROW and project traversing through SCDOT’s ROW. The data provided in this report are not intended for preparation of construction plan documents. No other warranty is made, express or implied. In the event that changes in the design or location of the alignment occur, the conclusions and recommendations contained herein should not be considered valid unless verified in writing by CDM Smith.

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Figure 1-1 Project Locus

(http://info2.scdot.org/GISMapping/Pages/OrderMaps.aspx)

Site Location

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Figure 1-2

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Section 2

Site and Subsurface Conditions

2.1 Site Conditions

2.1.1 General

The BJSWA Canal crossing site is located at the canal intersection of Highway 462 in Jasper

County, South Carolina. The surrounding area is generally rural and wooded. The ground cover at the crossing site consists of grass and asphalt roadways. Grades vary throughout the site from El.

+10 to +20.

2.1.2 Regional Geology

The project site is located in the Coastal Plain of South Carolina. Published Geologic mapping1 describes the site as Marine Delta Clay, Silt, Sand, and Gravel (mdb) in the Late Pleistocene (0.13 to 0.01 mya). This unit is described as “Light-gray to dark-brown kaolinitic marine clay, arkostic to quartzose sand, and gravel, intermixed and interbedded. Thickness 10-20 m, locally 35m where deposit fills channels eroded into underlying Tertiary deposits.” Soils encountered during our exploration were consistent with these descriptions.

2.2 Subsurface Investigation Program

As part of the C4 Improvements project, CDM Smith conducted a subsurface exploration on

January 5, 2022, to provide site-specific subsurface information for the proposed improvements.

2.2.1 Field Exploration

A geotechnical subsurface exploration was performed under the supervision of a licensed

Professional Engineer from CDM Smith. The drilling program consisted of three (3) test borings

(B-4 through B-6) drilled by Soil Consultants, Inc. (SCI) of Charleston, South Carolina. In general, the test borings were advanced using 4-inch-diameter mud rotary drilling techniques down to borehole termination depth, which ranged from 30 to 51.5 feet bgs.

The drill rig used for the exploration was a track-mounted CME-550X equipped with an automatic hammer having a measured hammer efficiency of 93%. The test borings were advanced using the rotary wash drilling technique with a tri-cone roller bit and temporary steel casing. A viscous slurry mixture consisting of extra high-yield bentonite clay and water was used to wash out the soil cuttings and maintain borehole wall stability during drilling operations.

The Standard Penetration Test (SPT) method was performed at test borings B-4, B-5, and B-6 in general accordance with Chapter 4.3.5 in the SCDOT GDM and ASTM D1586, Standard Test

Method for Penetration Test and Split Barrel Sampling of Soils. SPT testing and sampling was performed continuously from the existing ground surface to a depth of 20 feet to 26 feet and at 5-

1 Colquhoun, et. al., Quaternary geologic Map of the Savannah 4 degree x 6 degree quadrangle, United States, Quarternary

Geologic Atlas of the United States, Map I-1420 (NI-17), 1987

Section 2 • Site and Subsurface Conditions

2-2 foot-intervals thereafter to the depth of boring termination. Disturbed soil samples were collected at each SPT interval using a standard 2-inch O.D. and 30-inch-long split-spoon sampler.

The split-spoon sampler was driven with a 140-pound safety hammer falling 30-inches, and the number of blows required to drive the sampler was recorded for each 6-inch increment on the test boring logs. The sum of the second and third 6-inch increments represent the SPT N-Value.

The recovered split-spoon samples were visually classified in the field by CDM Smith in general accordance with ASTM D2488 Standard Practice for Description and Identification of Soils. Soil samples were later classified by Unified Soil Classification System (USCS) using ASTM D2487, and also American Association of State Highway and Transportation Officials (AASHTO M-145) soil designations, consistent with SCDOT GDM guidelines.

In addition to the split-spoon disturbed samples, three (3) undisturbed Shelby tube samples were collected in general accordance with ASTM D1587, Standard Practice for Thin-Walled Sampling of

Soils for Geotechnical Purposes. The Shelby tube samples were collected in test borings B-4 and

B-6. Thin-walled, steel Shelby tubes were hydraulically pushed into the soil then rotated to shear off the samples at the base of the Shelby tubes. After the Shelby tubes were removed from the test borings, they were immediately sealed and prepared for transport.

Groundwater levels at the test boring locations were estimated from the condition of samples obtained at the time of drilling. All test borings were backfilled with a grout mixture to the ground surface upon completion.

Upon completion of the drilling, CDM Smith licensed surveyors surveyed the as-drilled test boring locations and obtained: ground surface elevations, State Plane Northing and Easting coordinates, Global Positioning System (GPS) coordinates. Surveying was performed in accordance with the rules and regulations governing the practice of surveying in the state of South Carolina. The survey data are presented on the test boring logs in Appendix A.

2.2.2 Geotechnical Laboratory Test Results

Geotechnical laboratory tests were performed on select samples obtained from test borings B-4 through B-6 to assist with soil classification and to estimate the engineering properties of the materials. All laboratory testing was performed by SCI and consisted of the following:

Seven (6) moisture content tests were performed in accordance with ASTM D2216.

Three (4) wash of No. 200 sieve tests were performed in accordance with ASTM D1140.

Four (4) grain size analysis with wash of No. 200 sieve tests were performed in accordance with ASTM D6913.

Three (3) hydrometer tests were performed in accordance with ASTM D7928.

Seven (6) Atterberg limits tests were performed in accordance with ASTM D4318.

One (1) Standard Proctor test was performed in accordance with ASTM D698.

Two (2) One-Dimensional consolidation tests were performed in accordance with ASTM

D2435.

2-3

Two (1) Unconsolidated Undrained Triaxial tests were performed in accordance with ASTM

D2850.

One (2) Consolidated Undrained Triaxial with Pore Pressure test was performed in accordance with ASTM D4767.

A summary of the geotechnical laboratory index test results is presented in Table 2-1. The geotechnical laboratory test results are included in Appendix B.

2.3 Subsurface Conditions

2.3.1 General

Soils encountered during our field exploration were fill soils related to the roadway embankment and existing culvert, as well as Coastal Plain soils. The following sections provide a brief description of soils. See Appendix A for full description of soils. A summary of the soil conditions encountered in the test borings is included in Table 2-2.

2.3.2 Subsurface Conditions

2.3.2.1 Fill

Fill was encountered at the ground surface at all test boring locations (B-4 through B-6). The fill layer was between 2 and 7.5 feet thick at the test boring locations. The layer typically consisted of moist to wet, loose to dense Silty SAND, or very soft to stiff CLAY with varying amounts of sand.

SPT N-values in this layer ranged between 5 and 18 with an average of about 11. Fill material was encountered between approximately EL 12.5 to 20.3.

2.3.2.2 Coastal Plain

The Coastal Plain layer was encountered below the fill layer at all test boring locations (B-4 through B-6). All borings were terminated within the Coastal Plain layer penetrating between 26 and 44 feet of the layer. The layer typically consisted of moist to wet, very loose to dense, Poorly

Graded, Silty, or Clayey SAND, and very soft to soft Silt or Elastic SILT or Soft Fat CLAY or Lean

CLAY with varying amounts of sand. SPT N-values in this layer ranged between 0 and 37 with an average of about 9.

2.3.2.3 Groundwater Levels

Due to the rotary wash method of drilling conducted at the site, groundwater could not be determined at the time of boring. Based on the moisture conditions of soil samples recorded during drilling, the groundwater elevation is likely to be similar to the water surface elevation of the canal. Wet samples were observed starting at approximate El. +16 feet. Borings were backfilled with bentonite and cement upon completion.

It should be noted that fluctuations in rainfall, evaporation, construction activity, surface runoff, and other site-specific factors could cause groundwater elevations at the time of construction to vary from those observed during the subsurface exploration.

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2.4 Expected Variations in Subsurface Conditions

The interpretation of general subsurface conditions presented herein is based on soil and groundwater conditions observed at the test boring locations. However, subsurface conditions may vary between test boring locations. However, subsurface conditions may vary between test boring locations. If conditions are found to be different from those described herein, recommendations contained in this report should be reevaluated by CDM Smith and confirmed in writing.

Water levels are expected to fluctuate with canal level, season, temperature, climate, construction in the area, and other factors. Actual conditions during construction may be different from those observed at the time of the test borings.

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Table 2-1 Geotechnical Laboratory Index and Corrosion Test Results

Test Boring

Number

Sample

Number

Sample Depth

(ft)

USCS

Classification (1)

Moisture

Content (2)

Atterberg Limits (3) Sieve Analysis (4) Corrosion Tests

LL PL PI % Gravel % Sand

% Fines Resistivity (5)

(Ohm-cm)

Sulfate (6)

(% by mass)

Chloride (7)

(ppm) pH (8)

% Silt % Clay

B-4 S-5 8-10 -- --- --- --- --- --- --- 41.4 --- --- --- ---

B-4 U-1 16-18 MH 69.8 52 35 17 0 12.7 87.3 --- --- --- ---

B-4 S-10 20-22 -- 27.8 --- --- --- --- --- 12.7 --- --- --- ---

B-5 S-3 4-6 -- --- --- --- --- --- --- 74.6 --- --- --- ---

B-5 S-7 12-14 CH 28.7 102 34 68 --- --- 91 --- --- --- ---

B-6 Bulk-1 0-5 SM 15.3 18 16 2 0 56.2 43.8 --- --- --- ---

B-6 U-1 6-7 CH 41.3 56 28 28 --- 20.5 79.5 --- --- --- ---

B-6 U-2 12-14 SP-SC 19.3 --- --- --- --- 92.3 7.7 --- --- --- ---

B-6 S-8 18-20 -- --- --- --- --- --- --- --- 1,400 0.312 <10 4.7

Notes:

Abbreviations:

1 USCS classifications were performed in accordance with ASTM D2487. --- Test Not Performed CL Lean Clay

2 Moisture content tests were performed in accordance with ASTM D2216. ft Feet CH Fat Clay 3 Atterberg limits tests were performed in accordance with ASTM D4318. LL Liquid Limit MH Elastic Silt 4 Sieve analyses performed in accordance with ASTM D6913. PL Plastic Limit SC Clayey Sand 5 Soil resistivity tests were performed in accordance with ASTM G57. PI Plasticity Index SM Silty Sand 6 Sulfate content tests were performed in accordance with ASTM C1580. USCS Unified Soil Classification System SP-SC Poorly Graded Sand-Sandy Clay

7 Chloride content tests were performed in accordance with ASTM D512. ND Not Determined

8 pH tests were performed in accordance with ASTM G51. NP Non-Plastic cm Centimeter ppm Parts Per Million mV Millivolts

< Less Than

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Table 2-2 Subsurface Investigation Program

Test Boring Number Approximate Ground

Surface Elevation (ft) (1)

Exploration Depth (ft bgs) (2)

Approximate

Groundwater Elevation

(ft)

Layer Thickness (ft)

Fill Coastal Plain

B-4 18.7 30 NA 4 >26

B-5 20.3 51.5 NA 7.5 >44

B-6 19.3 31.5 NA 2 >29.5

Notes:

1 Elevations are in feet and referenced to the National American Vertical Datum of 1988 (NAVD88).

2 Indicated depths are depths below ground surface at the time of drilling.

Abbreviations:

> Indicates layer not fully penetrated bgs Below ground surface ft Feet

NA Not Apparent

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3-1

Section 3

Geotechnical Engineering Evaluation and Design

Recommendations

3.1 General

Geotechnical engineering evaluations have been made as they relate to the proposed C4

Improvements in Jasper County, South Carolina. In general, these evaluations are based on the results of the subsurface investigation described in Section 2 of this report. In addition, recommended design criteria are based on performance tolerances, such as allowable settlement, as understood to relate to similar structures.

3.2 Foundation Design Recommendations

3.2.1 General

Based on the proposed box culvert location, depth, and dimensions, it is likely that the excavation for the box culverts may encounter loose or very soft fill and/or Coastal Plain soils. The existing soils along the box culvert are generally not considered suitable for support of the proposed box culvert. We recommend over-excavation and replacement to a limited depth below the box culvert.

3.2.2 Seismic Hazard Analyses

A seismic hazard analysis has been conducted using methodologies from the SCDOT’s

Geotechnical Design Manual, Chapter 13. Peak ground accelerations for the FEE (15% in 75 years) and SEE (3% in 75 years) were taken from the United States Geological Survey’s (USGS)

Unified Hazard Tool. Peak ground acceleration for the SEE was 0.2522g and the moment magnitude is 7.3. Peak ground acceleration for the FEE was 0.0652g and the moment magnitude is 7.1. Results of the analyses reveal that there will not be a seismic vulnerability on this crossing during either the FEE or the SEE. USGS uses a return period of 475 years (10% in 50 years) and

2475 years (2% in 50 years) for the FEE and SEE, which are roughly equal to the above frequencies.

3.2.3 Over-excavation and Replacement

Based on the soils observed in soil test borings, we recommend removal of unsuitable materials below the box culvert to El. +9 (approximately 3 feet of undercut) and replacement with compacted crushed stone to the bearing elevation of the box culvert. Additional depth of excavation and replacement may be required to remove unsuitable soils present at the excavated subgrade. A geotextile fabric should be placed between the fine-grained subgrade soils and the stone to prevent the migration of fines.

Compacted crushed stone should extend at least two feet beyond the edge of the box culvert exterior, then outward and downward at a slope of one horizontal to one vertical (1H:1V) to the suitable bearing soils below.

Section 3 • Geotechnical Engineering Evaluation and Design Recommendations

3-2

Based on our evaluation of settlement of the box culvert after over-excavation and replacement, total elastic settlements are expected to be less than two inches. The majority of the settlement is expected to occur during construction. Long term consolidation is expected to be up to about 2 inches over the following 10 years. We estimate about 1.6 inches of settlement on the upstream side of the culvert where up to 10 feet of new fill is to be placed. We estimate settlement on the downstream side of the culvert to be about 0.6 inches for the 9 feet of fill that will be placed. Most of the settlement will occur outside of the SCDOT right of way. Settlement near the roadway should be minimal as the weight of the material that will be placed is less than the material that is to be removed. Maximum differential settlement will be about 1.6 inches over about 40 feet of the culvert length.

All embankments and roadway structures should be designed to tolerate the full magnitude of this settlement.

3.2.4 Excavation Backfill

Within 10 feet of either side and up to the top of the box culvert, the backfill should consist of select common fill placed and compacted to at least 95 percent of the standard Proctor maximum dry density as determined by ASTM D698. The remaining backfill up to the finished grades, should consist of structural fill, common, or select common fill as specified or indicated.

Where the excavation is within the roadway limits, structural fill should be placed and compacted to at least 95 percent of the standard Proctor maximum dry density as determined by ASTM D698 up to the pavement subgrade. Where the excavation is within roadway limits, restoration of the pavement subgrade and paving should be consistent with the existing roadways. In non-paved areas, the excavation should be backfilled using common fill and placed and compacted to at least

92 percent of standard Proctor maximum dry density as determined by ASTM D698.

The excavated soils may be used for back fill provided they meets the requirements on select common fill or common fill.

3.2.5 Corrosion Considerations

SCI performed environmental corrosion testing on select soil samples collected for this project.

Environmental corrosion testing included parameters such as pH (acidity) in accordance with

ASTM G51, resistivity in accordance with ASTM G51, chloride content (Cl) in accordance with

ASTM D-512, and sulfate content (SO4) in accordance with ASTM C1580. Based on the laboratory test results, the environment near the proposed pipelines can be classified as high risk for corrosion. To increase the service life of the sheet piles, protective measures such as coatings, cathodic protection, or sacrificial thickness shall be included.

The results of the environmental corrosion testing are included in Table 2-1 and in Appendix B.

3.3 Pavement Replacement

Design of the pavement along HWY 462 is not within the scope of this report, however, online records indicate that the pavement along newer sections of US321 consist of about 10-inches of hot mix asphalt. This typical section will be incorporated into the Construction Drawings and included for SCDOT review.

Section 3 • Geotechnical Engineering Evaluation and Design Recommendations

3-3

3.4 Sheet Pile Wing-Walls

The wingwalls of the will be extended at both the upstream and downstream sides of the box culvert. The sheet pile walls will extend 10 ft to 16 feet beyond the box culvert apron and wingwalls with a maximum exposed wall height of 8 feet plus 4 feet of stick up. The sheet pile will be constructed using PZ-22 (or similar) sheet piles driven to a minimum tip at El. -7. The sheet pile wall was design for active and passive soil pressures, a 288 psf surcharge load, and a groundwater at El. +15. The wall will have draining materials and weepholes along the back side of the wall to reduce the potential for differential water levels.

Based on our evaluation, the free-head deflection of the sheet pile wall, under the anticipated loads and designed as recommended above, are expected to be less than 0.3-inch. Heavy grading equipment that could impose temporary excessive pressures or long-term excessive residual pressures against the constructed walls will not be permitted within about 5 feet (horizontally) of the walls.

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Section 4

Construction Considerations

4.1 General

The purpose of this section is to discuss issues related to geotechnical aspects of construction as required for development of the contract documents. Included are anticipated methods of construction required to achieve the recommendations presented herein and identification of potential construction-related issues.

The Contractor will be required to base their construction methods and cost estimates on an independent interpretation of the subsurface conditions.

4.2 Excavation and Excavation Support

We anticipate that excavations for the box culvert can made using conventional earthmoving equipment with open cut and/or excavation support systems.

Excavations for the box culvert are anticipated to encounter fill and Coastal Plain soil layers and extend up to approximately 16 feet below existing grade. Excavation should not extend into the zone of influence of any existing structures without an excavation support system or underpinning that has been prepared by a Professional Engineer licensed in the State or South

Carolina and submitted to the Engineer for review. The zone of influence is defined as extending 2 feet beyond the bottom exterior edge of the existing foundation then down and away at a 1H:1V or at a 1H:1V slope from the springline of the utilities. Undermining of existing foundations must not occur.

The Contractor will be responsible for conducting the excavation work in accordance with the applicable federal and state laws and regulations, including Occupational Safety and Health

Administration (OSHA). Where open excavations are feasible, the side slopes should be designed in accordance with OSHA regulations. The Contractor should be responsible for selection and the design of the means and methods for excavation and excavation support such as open cut with stable side slopes, trench box, soldier pile and lagging, etc.

Use of excavation support may limit the amount of excavation spoils and serve to protect adjacent structures, utilities, and roadways. Selection of the excavation support systems will likely be dependent upon subsurface layers, groundwater conditions, adjacent structures, surcharge loading, etc. The Contractor should develop an excavation plan, including excavation support systems designed by a Professional Engineer licensed in the State of South Carolina. Additional design considerations may be required based on the Contractor’s planned construction methods.

4.3 Dewatering

The Contractor will be responsible to design and implement a dewatering and drainage system that maintains a stable, undisturbed subgrade that is free of groundwater and surface water during all construction activities. It is anticipated that the excavations will extend below the

Section 4 • Construction Considerations

4-2 design groundwater level based on the observed water levels in the canal. The design of the dewatering system shall be performed by a Professional Engineer licensed in the State of South

Carolina. To avoid disturbance of the subgrade, the water level in all excavations shall be maintained at least 2 feet below the lowest excavation subgrade elevation during the entire period of excavation and fill placement.

Where applicable, the dewatering system shall be designed in conjunction with an excavation support system selected by the Contractor. Depending on the depth of the excavation and excavation support system selected, wells, well points, and/or pumping from open sumps within the excavation may be required. Wells, well point, and sumps shall be adequately filtered to avoid loss of fines. The site should be graded to direct surface runoff away from excavations.

The Contractor must be prepared to operate the dewatering system continuously, as required to complete the work and avoid floatation or uplift prior to completion of the facility. During periods where failure of the system would adversely impact work completed, the Contractor shall provide a back-up system to ensure continuous operation.

The Contractor must design the dewatering system to not adversely impact adjacent structures, utilities, roadways, or site features. All dewatering, handling and disposal of pumped water and any special testing shall be conducted in accordance with local regulations, permits and specified requirements.

4.4 Protection and Preparation of Subgrade Soils

Care shall be taken to avoid excess traffic on the excavated subgrade prior to placement of the structural fill, or crushed stone. The exposed subgrade surface should be protected against precipitation, and the subgrade should not be allowed to freeze. Under no circumstances should fill or foundation concrete be placed on a disturbed, wet, or frozen subgrade.

Granular soil subgrades shall be proof rolled with a vibratory compactor for at least four (4) passes for the structures and two passes prior to placement of fill or crushed stone. If fine grained materials are anticipated at subgrade, the final six inches of the excavation should be performed by smooth-edge bucket. Any unsuitable material encountered at the subgrade level should be removed and replaced with compacted crushed stone wrapped in geotextile fabric as recommended herein.

4.5 Protection of Adjacent Structures

4.5.1 General

Some excavation for the proposed box culvert may be made within the zone of influence of existing roadways, and utilities. Protection of existing roadways and utilities is the responsibility of the Contractor. The construction procedures undertaken shall be performed in a manner that does not negatively affect the existing facilities.

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4.6 Backfill

4.6.1 Structural Fill

Structural fill should consist of a mineral soil free of organic material, loam, debris, frozen soil, or other deleterious material which may be compressible, or which cannot be properly compacted.

Structural fill should conform to the following gradation requirements in Table 4-1.

Table 4-1 Structural Fill Gradation

U.S. Standard Sieve Size Percent Passing by Weight

3 inches 100

No. 4 20 to 70

No. 40 5 to 35

No. 200 0 to 10

Structural fill should have a maximum a maximum dry density of at least 100 pcf as determined by SC-T-29. Liquid limit shall be no more than 40 percent by weight, as specified in ASTM D4318.

Structural fill should be placed in maximum 8-inch-thick loose lifts and compacted with suitable compaction equipment to at least 95 percent of the maximum dry density as determined by ASTM

D698. Lift thickness should be reduced to 4 inches in confined areas accessible only to hand-guided compaction equipment. Structural fill should be placed between minus two and plus three percent of its optimum moisture content.

4.6.2 Common Fill and Select Common Fill

Common fill should consist of soil free of roots, vegetative matter, organic material, topsoil, loam, waste, debris, highly micaceous silt, frozen soil, or other objectionable material. It should not contain stone blocks, broken concrete, masonry rubble, or other similar materials. It should have physical properties such that it can be readily spread and compacted. It should contain stones no larger than six inches, have no more than 75 percent of material passing the No. 200 sieve, and a maximum dry density of at least 90 pcf as determined by ASTM D698.

Select common fill should meet the requirements listed above but should contain stones no larger than 3 inches.

Common fill or select common fill shall be placed in maximum 8-inch-thick lifts, as placed, and compacted with suitable compaction equipment to at least 92 and 95 percent, respectively, of the maximum dry density as determined by ASTM D698. Lift thickness should be reduced to 6 inches in confined areas accessible only to hand-guided compaction equipment. Common fill and select common fill should be placed within minus three to plus three percent of its optimum moisture content.

4.6.3 Crushed Stone

Crushed stone should consist of hard, durable, angular or subangular particles of proper size and gradation, and should be free of sand, loam, clay, excess fines, and other deleterious materials.

4-4

The material should be graded in accordance with size No. 57 in accordance with ASTM D448

(SCDOT Standard Size No. 57).

Crushed stone should be placed in maximum 6-inch-thick lifts, as placed.

4.7 Geotextile Fabric

A non-woven geotextile fabric should be used to separate crushed stone from underlying subgrade soils to prevent migration of fines. The geotextile fabric should be Mirafi 160N or approved equivalent.

4.8 Construction Monitoring

It is recommended that a qualified Geotechnical Engineer or experienced technician under the direction of the Geotechnical Engineer be present during construction to confirm that the

Contractor complies with the intent of these recommendations. Specifically, the field representative would undertake the following responsibilities:

Monitor the excavation and installation and performance of excavation support systems.

Confirm that appropriate dewatering and surface water control methods are employed.

Confirm the removal of unsuitable materials present at foundation subgrade level and replacement with proper backfill material.

Confirm that the subgrades are prepared, and conditions encountered are suitable for support of the proposed structures.

Observe, test and document placement and compaction of backfill material, where appropriate. Samples of imported fill should be submitted to the Engineer for approval prior to starting this work.

In addition, the field representative would be present to identify and provide response should conditions encountered differ from those assumed during preparation of this report.

4-5

Appendix A

USCS Legend

Test Boring Logs

Hammer Efficiency Report

GC

GM

GP

GW

DESCRIPTIONS

TYPICAL

LETTERGRAPH

SYMBOLS

MAJOR DIVISIONS

SOIL CLASSIFICATION CHART

NOTE: DUAL SYMBOLS ARE USED TO INDICATE BORDERLINE SOIL CLASSIFICATIONS

LIQUID LIMIT

GREATER THAN 50

LIQUID LIMIT

LESS THAN 50

(APPRECIABLE AMOUNT

OF FINES)

SANDS WITH

FINES

U S

C S

L

E G

E N

D

/3

/2

PT

OH

CH

MH

OL

CL

ML

SC

SM

SP

WELL GRADED GRAVELS, GRAVEL -

SAND MIXTURES, LITTLE OR NO

FINES

PEAT, HUMUS, SWAMP SOILS WITH

HIGH ORGANIC CONTENTS

ORGANIC CLAYS OF MEDIUM TO

HIGH PLASTICITY, ORGANIC SILTS

INORGANIC CLAYS OF HIGH

PLASTICITY

INORGANIC SILTS, MICACEOUS OR

DIATOMACEOUS FINE SAND OR

SILTY SOILS

ORGANIC SILTS AND ORGANIC

SILTY CLAYS OF LOW PLASTICITY

INORGANIC CLAYS OF LOW TO

MEDIUM PLASTICITY, GRAVELLY

CLAYS, SANDY CLAYS, SILTY

CLAYS, LEAN CLAYS

INORGANIC SILTS AND VERY FINE

SANDS, ROCK FLOUR, SILTY OR

CLAYEY FINE SANDS OR CLAYEY

SILTS WITH SLIGHT PLASTICITY

CLAYEY SANDS, SAND - CLAY

MIXTURES

SILTY SANDS, SAND - SILT

MIXTURES

POORLY GRADED SANDS,

GRAVELLY SAND, LITTLE OR NO

FINES

WELL GRADED SANDS, GRAVELLY

SANDS, LITTLE OR NO FINES

CLAYEY GRAVELS, GRAVEL - SAND -

CLAY MIXTURES

SILTY GRAVELS, GRAVEL - SAND -

SILT MIXTURES

POORLY GRADED GRAVELS,

GRAVEL - SAND MIXTURES, LITTLE

OR NO FINES

(LITTLE OR NO FINES)

CLEAN SANDS

(APPRECIABLE AMOUNT

OF FINES)

GRAVELS WITH

FINES

(LITTLE OR NO FINES)

CLEAN

GRAVELS

HIGHLY ORGANIC SOILS

SILTS

AND

CLAYS

SILTS

AND

CLAYS

MORE THAN 50%

OF COARSE

FRACTION

PASSING ON NO. 4

SIEVE

SAND

AND

SANDY

SOILS

MORE THAN 50%

OF COARSE

FRACTION

RETAINED ON NO.

4 SIEVE

GRAVEL

AND

GRAVELLY

SOILS

MORE THAN 50%

OF MATERIAL IS

SMALLER THAN

NO. 200 SIEVE SIZE

FINE

GRAINED

SOILS

MORE THAN 50%

OF MATERIAL IS

LARGER THAN NO.

200 SIEVE SIZE

COARSE

GRAINED

SOILS

SW

U-1

SS

SS

SS

SS

SS

SS

SS

SS

ST

SS

SS

SS

Dry, M. Dense, black and gray, Silty fine

SAND (SM / A-2-4)

Dry, M. Dense, gray, Poorly Graded fine

SAND (SM / A-2-4)

Wet, Loose, gray and brown, Silty fine

SAND (SM / A-2-4)

Fine to coarse, little clay

Wet, Loose, gray, Clayey fine SAND (SC / A-2-6), with clay layers

-medium to coarse, trace gravel

Wet, V. Soft, dark gray, Elastic SILT with Sand (MH / A-7-5) interbedded with sand

Wet, V. Loose, dark gray, Silty SAND (SM / A-2-4)

Wet, V. Soft, dark gray, Elastic SILT with Sand (MH / A-7-5) interbedded with sand

Wet, V. Loose, dark gray, Silty SAND (SM / A-2-4), interbedded with Fat Clay

- Medium to coarse

Wet, V. Loose to M. Dense, dark gray, Silty coarse SAND (SM / A-2-4)

F il l

C o a s ta l P la in

TV=1.5, PP=0.25

TV=0

PP=0

P

WOH

WOH

U

WOH

WOH

S

WOH

WOH

H

NA

Station, Offset

NA , NA

Northing, Easting:

190776.48, 2024166.9

Hammer ETR 93%

Boring Number:

B-4

Sheet 1 of 2

Client: BJWSA

Project Location: Jasper County, SC

Project Name: Chelsea Canal

Project Number: 266799

Depth Date Time

Depth to Initial Water Level (ft):

Drilling Contractor/Driller: SCI / Bubba

Hammer Weight/Drop Height/ Spoon Size: 140 lbs lb / 30 in /2 in O.D.

Surface Elevation (ft.): 18.7

Total Depth (ft.): 30

Logged By: T. Evans

Abandonment Method: Concrete and Bentonite

NA NA

Drilling Method/Casing/Core Barrel Size: Drive and Wash / NA in / NA

NA

Bore Hole Location: SC 462

Drilling Date: Start: 1/5/2022 End: 1/5/2022

S a m p le

N u m b e r

B lo w s p e r i n c h e s

S a m p le

R e c o v e ry in

G ra p h ic L o g

S tr a ta

S a m p le

L e n g th in

RemarksMaterial Description

Elev.

Depth

(ft)

S a m p le

T y p e

N -V a lu e

Burmister ClassificationSample Types Consistency vs Blowcount/Foot

Granular (Sand): Fine Grained (Clay):

Dense: 30-50 V. Dense: >50

V. Loose: 0-4 Loose: 4-10 M. Dense: 10-30

V. Soft: <2 Soft: 2-4 M. Stiff: 4-8

Stiff: 8-15 V. Stiff: 15-30 Hard: >30 and 35-50% some 20-35% little 10-20% trace <10% moisture, density, color

HP - Hydro Punch SS - Split Spoon ST - Shelby Tube WS - Wash Sample GP - Geoprobe

AS - Auger/Grab Sample CS - California Sampler BQ - 1.5" Rock Core NQ - 2" Rock Core

B L

J W

S A

C A

N A

L C

R O

S S

IN

G

.1

.2

.G

P J

/2

/2

Boring Number: B-4Date: 7/18/2022Reviewed by: T. Evans

18.7

13.7

8.7

3.7

-1.3

-6.3

12SS 24 13 - Light gray

Test boring teminated at 30.0 feet bgs.

Note:

'PP' - Pocket Penetrometer (TSF) 'TV' - Torvane (TSF)

C o a s ta l P la in

S a m p le

N u m b e r

B lo w s p e r i n c h e s

S a m p le

R e c o v e ry in

G ra p h ic L o g

S tr a ta

S a m p le

L e n g th in

RemarksMaterial Description

Elev.

Depth

(ft)

S a m p le

T y p e

N -V a lu e

Boring Number: B-4

Boring Number:

B-4

Sheet 2 of 2

Client: BJWSA

Project Location: Jasper County, SC

Project Name: Chelsea Canal

Project Number: 266799

W

S A

C A

N A

L C

R O

S S

IN

G

.1

.2

.G

P J

/2

/2

-6.3

-11.3

-16.3

-21.3

-26.3

-31.3

-36.3

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

Moist, Stiff, mottled gray and red-brown, Sandy Lean CLAY (CL / A-6), thin sand layers

Moist, Loose, dark gray, Silty SAND (SM / A-2-4)

Wet, Soft, dark gray, Sandy Fat CLAY (CH / A-7), some silt

Moist, M. Stiff, mottled gray and orange, fine Sandy lean CLAY (CL / A-6)

Wet, M. Dense, dark gray, Silty SAND (SM / A-2-4)

- Loose, light gray

Wet, Soft, blue-gray, Fat CLAY (CH / A-7-5)

Wet, Loose, gray, Silty medium SAND (SM / A-2-4)

- Clean SAND (SP / A-3)

Wet, Soft, dark gray, Sandy Lean CLAY (CL / A-6), interbedded sand layers

Wet, Loose, dark gray, Silty SAND (SM / A-2-4)

- V. Loose, trace shells

- Fine to coarse

F il l

C o a s ta l P la in

TV=1.5

PP=0.5

TV=4.5

PP=1

TV=3.5

PP=1

TV=3

PP=0.5

TV=1

PP=0.04

WOH

Station, Offset

NA , NA

Northing, Easting:

190681.55, 2024280.03

Hammer ETR 93%

Boring Number:

B-5

Sheet 1 of 2

Client: BJWSA

Project Location: Jasper County, SC

Project Name: Chelsea Canal

Project Number: 266799

Depth Date Time

Depth to Initial Water Level (ft):

Drilling Contractor/Driller: SCI / Bubba

Hammer Weight/Drop Height/ Spoon Size: 140 lbs lb / 30 in /2 in O.D.

Surface Elevation (ft.): 20.3

Total Depth (ft.): 51.5

Logged By: T. Evans

Abandonment Method: Concrete and Bentonite

NA NA

Drilling Method/Casing/Core Barrel Size: Drive and Wash / NA in / NA

NA

Bore Hole Location: SC 462

Drilling Date: Start: 1/5/2022 End: 1/5/2022

S a m p le

N u m b e r

B lo w s p e r i n c h e s

S a m p le

R e c o v e ry in

G ra p h ic L o g

S tr a ta

S a m p le

L e n g th in

RemarksMaterial Description

Elev.

Depth

(ft)

S a m p le

T y p e

N -V a lu e

Burmister ClassificationSample Types Consistency vs Blowcount/Foot

Granular (Sand): Fine Grained (Clay):

Dense: 30-50 V. Dense: >50

V. Loose: 0-4 Loose: 4-10 M. Dense: 10-30

V. Soft: <2 Soft: 2-4 M. Stiff: 4-8

Stiff: 8-15 V. Stiff: 15-30 Hard: >30 and 35-50% some 20-35% little 10-20% trace <10% moisture, density, color

HP - Hydro Punch SS - Split Spoon ST - Shelby Tube WS - Wash Sample GP - Geoprobe

AS - Auger/Grab Sample CS - California Sampler BQ - 1.5" Rock Core NQ - 2" Rock Core

W

S A

C A

N A

L C

R O

S S

IN

G

.1

.2

.G

P J

/2

/2

Boring Number: B-5Date: 7/18/2022Reviewed by: T. Evans

20.3

15.3

10.3

5.3

0.3

-4.7

SS

SS

SS

SS

SS

SS

- Dense, coarse, little gravel

Moist, Loose, greenish gray, Silty fine SAND (SM / A-2-4), trace wood and fibers

Moist to dry, Stiff, greenish gray, SILT with Sand (ML / A-4)

Dry, Loose, greenish gray, Silty fine SAND

(SM / A-2-4)

Test boring teminated at 51.5 feet bgs.

Note:

'PP' - Pocket Penetrometer (TSF) 'TV' - Torvane (TSF)

C o a s ta l P la in

TV=2.5

PP=1.5

TV=3.75

PP=0.25

S a m p le

N u m b e r

B lo w s p e r i n c h e s

S a m p le

R e c o v e ry in

G ra p h ic L o g

S tr a ta

S a m p le

L e n g th in

RemarksMaterial Description

Elev.

Depth

(ft)

S a m p le

T y p e

N -V a lu e

Boring Number: B-5

Boring Number:

B-5

Sheet 2 of 2

Client: BJWSA

Project Location: Jasper County, SC

Project Name: Chelsea Canal

Project Number: 266799

W

S A

C A

N A

L C

R O

S S

IN

G

.1

.2

.G

P J

/2

/2

-4.7

-9.7

-14.7

-19.7

-24.7

-29.7

-34.7

U-1

U-2

SS

SS

SS

ST

SS

SS

ST

SS

SS

SS

Moist, M. Dense, mottled gray and brown, Silty SAND (SM / A-4), interbedded sand

Moist, Stiff, mottled orange and gray, Lean CLAY (CL / A-6), interbedded sand

- M. Stiff

Moist, mottled orange and gray, Sandy Fat CLAY (CH / A-7-6) interbedded sand

Wet, Loose, mottled gray and orange, Poolry Graded fine to medium SAND with Clay (SP-SC / A-2-6)

- Trace clay balls

- Fine to medium, alternating layers of gray and brown sand

- M. Dense, fine

Wet, Soft, blue-gray, Lean CLAY (CL / A-6)

Wet, M. Dense, gray, Silty medium to coarse

SAND (SM / A-2-4)

F il l

C o a s ta l P la in

TV=1.5

PP=2

TV=4.75

PP=0.5

TV=5

PP=0.6

TV=1.5

PP=0.5

TV=0.5

PP=0.09

P

P

U

U

S

S

H

H

NA

NA

Station, Offset

NA , NA

Northing, Easting:

190683.08, 2024389.45

Hammer ETR 93%

Boring Number:

B-6

Sheet 1 of 2

Client: BJWSA

Project Location: Jasper County, SC

Project Name: Chelsea Canal

Project Number: 266799

Depth Date Time

Depth to Initial Water Level (ft):

Drilling Contractor/Driller: SCI / Bubba

Hammer Weight/Drop Height/ Spoon Size: 140 lbs lb / 30 in /2 in O.D.

Surface Elevation (ft.): 19.3

Total Depth (ft.): 31.5

Logged By: T. Evans

Abandonment Method: Concrete and Bentonite

NA NA

Drilling Method/Casing/Core Barrel Size: Drive and Wash / NA in / NA

NA

Bore Hole Location: SC 462

Drilling Date: Start: 1/5/2022 End: 1/5/2022

S a m p le

N u m b e r

B lo w s p e r i n c h e s

S a m p le

R e c o v e ry in

G ra p h ic L o g

S tr a ta

S a m p le

L e n g th in

RemarksMaterial Description

Elev.

Depth

(ft)

S a m p le

T y p e

N -V a lu e

Burmister ClassificationSample Types Consistency vs Blowcount/Foot

Granular (Sand): Fine Grained (Clay):

Dense: 30-50 V. Dense: >50

V. Loose: 0-4 Loose: 4-10 M. Dense: 10-30

V. Soft: <2 Soft: 2-4 M. Stiff: 4-8

Stiff: 8-15 V. Stiff: 15-30 Hard: >30 and 35-50% some 20-35% little 10-20% trace <10% moisture, density, color

HP - Hydro Punch SS - Split Spoon ST - Shelby Tube WS - Wash Sample GP - Geoprobe

AS - Auger/Grab Sample CS - California Sampler BQ - 1.5" Rock Core NQ - 2" Rock Core

W

S A

C A

N A

L C

R O

S S

IN

G

.1

.2

.G

P J

/2

/2

Boring Number: B-6Date: 7/18/2022Reviewed by: T. Evans

19.3

14.3

9.3

4.3

-0.7

-5.7

SS

SS

Test boring teminated at 31.5 feet bgs.

Note:

'PP' - Pocket Penetrometer (TSF) 'TV' - Torvane (TSF)

C o a s ta l P la in

S a m p le

N u m b e r

B lo w s p e r i n c h e s

S a m p le

R e c o v e ry in

G ra p h ic L o g

S tr a ta

S a m p le

L e n g th in

RemarksMaterial Description

Elev.

Depth

(ft)

S a m p le

T y p e

N -V a lu e

Boring Number: B-6

Boring Number:

B-6

Sheet 2 of 2

Client: BJWSA

Project Location: Jasper County, SC

Project Name: Chelsea Canal

Project Number: 266799

W

S A

C A

N A

L C

R O

S S

IN

G

.1

.2

.G

P J

/2

/2

-5.7

-10.7

-15.7

-20.7

-25.7

-30.7

-35.7

Drill Rig: CME 45C Test Date: 12/16/2021 Boring ID: TB-1

Hammer: Automatic Project No. : Rod Type: BW

Rig Operator: Grimball Location: SCI Yard Analyzer ID: 216BW

Engineer: Henderson Drilling Method: Mud Rotary Rod Area: 1.82 in2

Depth: 40 ft Depth: 45 ft Depth: 50 ft

LE: 43 ft LE: 48 ft LE: 53 ft

Blow Count: 1, 1, 2 Blow Count: 5, 11, 21 Blow Count: 8, 17, 17

Blow No. Energy Blow No. Energy Blow No. Energy Blow No. Energy Blow No. Energy Blow No. Energy

1 0.326 26 1 0.343 26 0.328 1 0.333 26 0.320

2 0.323 27 2 0.333 27 0.338 2 0.332 27 0.327

3 0.321 28 3 0.333 28 0.340 3 0.333 28 0.321

4 0.316 29 4 0.330 29 0.329 4 0.331 29 0.325

5 30 5 0.330 30 0.336 5 0.338 30 0.320

6 31 6 0.330 31 0.335 6 0.328 31 0.329

7 32 7 0.326 32 0.341 7 0.328 32 0.325

8 33 8 0.329 33 0.341 8 0.321 33 0.323

9 34 9 0.328 34 0.339 9 0.322 34 0.326

10 35 10 0.330 35 0.338 10 0.319 35 0.326

11 36 11 0.323 36 0.338 11 0.322 36 0.318

12 37 12 0.329 37 0.335 12 0.325 37 0.317

13 38 13 0.321 38 13 0.319 38 0.332

14 39 14 0.325 39 14 0.329 39 0.324

15 40 15 0.332 40 15 0.321 40 0.326

16 41 16 0.329 41 16 0.317 41 0.321

17 42 17 0.325 42 17 0.320 42 0.323

18 43 18 0.328 43 18 0.316 43

19 44 19 0.328 44 19 0.313 44

20 45 20 0.325 45 20 0.317 45

21 46 21 0.332 46 21 0.316 46

22 47 22 0.319 47 22…